Good conductivity is a high-performance feature of a semiconductor device. Because current and resistance are inversely related, using metal silicide on a semiconductor device can effectively reduce metal-oxide-semiconductor (MOS) transistor device contact resistance and achieve higher performance.
To improve performance of metal-oxide-semiconductor field-effect transistors (MOSFET), use of metal silicides is well known in the field of MOSFET fabrication.
U.S. Pat. No. 7,544,575 titled “Dual Metal Silicide Scheme Using A Dual Spacer Process” disclosed use of silicides to improve performance of the semiconductor device that comprises providing a polysilicon structure and source/drain regions formed adjacent to the polysilicon structure in which a dual silicide scheme is used to form first silicide regions in the polysilicon, source and drain regions using a first metal. After forming sidewall spacers, a second metal is used to form second silicide regions in the polysilicon, source and drain regions to reduce encroachment by the second silicide in the source/drain and to reduce resistance in the polysilicon structure caused by agglomeration and voiding the first silicide.
The second silicide regions usually use a metal such as nickel. A chemical reaction of nickel and silicon forms nickel silicide that has an advantage of low resistance. However nickel atoms spread very rapidly in silicon, easily react with the first silicide region and keep the first silicide from forming.